Israeli troops met fierce resistance from Hezbollah guerrillas Thursday as they crossed into Lebanon to seek tunnels and weapons for a second consecutive day. Israel, meanwhile, refused to rule out a full-scale invasion.

Israeli warplanes also launched new airstrikes on Beirut's southern suburbs, a Hezbollah stronghold, shortly after daybreak Thursday, followed by strikes in the guerrilla's heartland in the south and eastern Bekaa Valley.

The strikes came a wave of bombings Wednesday killed as many as 70 people, according to Lebanese television, making it the deadliest day since the fighting began on July 12.

Russia sharply criticized Israel over its onslaught against Lebanon, now in its ninth day, sparked when Hezbollah guerrillas captured two Israeli soldiers. The Russian Foreign Ministry said Israel's actions have gone "far beyond the boundaries of an anti-terrorist operation" and repeating calls for an immediate cease-fire.

At least 306 people have been killed in Lebanon since the Israeli campaign began, according to the security forces control room that collates casualties. In Israel, 29 people have been killed, including 14 soldiers. The U.N. has said at least a half million people have been displaced in Lebanon.

In developments on the evacuation of Lebanon, U.S. Marines landed in Beirut Thursday to help Americans onto a Navy ship bound for Cyprus in the second mass U.S exodus from the battle-torn country.

About 40 U.S. Marines arrived at a beach just north of Beirut in a landing craft and picked up 300 Americans who they ferried to the amphibious assault ship USS Nashville just off the coast. The Nashville is supposed to sail for Cyprus with about 1,000 Americans.

Hundreds of people, some with shirts draped over their heads to protect themselves from the sun, gathered on the beach. A U.S. Embassy official, speaking through a megaphone, pleaded for patience, reassuring the crowd that all those who registered to be evacuated would be assisted.

"We are frustrated and disappointed, but we are O.K.," said Bob Elazon, an Illinois resident who complained that the U.S. evacuation was badly organized.

Elazon, who left his native Lebanon 34 years ago, was with his 20-year-old daughter, Anna, who was visiting the country for the first time. His wife departed just before the fighting erupted.

Meanwhile, the first plane carrying U.S. evacuees landed outside Baltimore early Thursday, and eager family members waited to greet the 145 Americans aboard the charter flight from Cyprus.